This invention is concerned with improvements in magnetic deflection yokes used for electron beam deflection in cathode ray tubes generally of the display producing variety requiring relatively large angles of deflection and wherein the deflection field is short compared to the beam throw distance to the CRT faceplate. It is not applicable to those types commonly known as immersion field systems primarily used in image pickup (camera) devices.
The prior art has gradually evolved in response to requirements for larger deflection angles and high beam spot performance from a primarily cylindrical magnetic core to one using an annular magnetic core having a substantial front flare in which there is an increase in internal core diameter as a function of core length. The result is a more uniformly graded deflection field in the direction of the electron beam or z axis. The above evolution applies to use of two principal construction techniques. One uses solid smooth surfaced flared annular cores in conjunction with distributed (typically form wound) coil sets and/or toroidal windings. The other uses slotted flared annular stator cores. Either method of construction is applicable with the improvements to be described herein.
In a deflection yoke of either of the above types there is substantial magnetic field outside of the CRT, (hence out of the required deflection field region) due to both the diameter of the yoke and to its end turn and other external field distributions. These fields reduce efficiency of the yoke and, unless carefully controlled, they can introduce distortions of the electron beam. The various parts and windings must be controlled to a high degree of precision in order to provide a high resolution output display of the associated CRT.
Over many years of deflection yoke development, there has been no significant improvement in its efficiency and, in fact, the shift to flared core designs loses efficiency. It is the purpose of this invention to provide a substantial increase in deflection yoke efficiency. It is a further purpose to improve performance at the same time making construction of the main yoke assembly less critical.